Typically, in a digital reproduction device, a document or image is scanned by a digital scanner which converts the light reflected from the document into electrical charges representing the light intensity from predetermined areas (pixels) of the document. The pixels of image data are processed by an image processing system which converts the pixels of image data into signals which can be utilized by the digital reproduction machine to recreate the scanned image.
Sometimes the white regions in the original are not imaged as white regions in the produced document. Typically, digital scanning and multifunction devices provide the function of automatic background suppression to make white regions in the original white on scanned images or copies. The quality of background suppression is of great importance to many customers. Background detection and suppression in color systems is more challenging than in monochrome systems due to the more complex nature of the problem.
One method for background suppression is to perform the background suppression after the document processing system input is converted to a CIE Lab color space, where L* represents the luminosity, and a, b represent the chrominance components which define the difference between a color and a chosen reference color of the same intensity. Typically, the colored document is scanned by a scanner using a set of red, green, and blue (RGB) sensors which produces a data representation in terms of the RGB signals at each pixel location. The data is then converted into a luminance/chrominance space.
Background suppression is often performed in the chrominance channels. However, since chrominance channels tend to get adjusted independently of other pixel's chrominance and also independently of the luminance, a color shift tends to occur in some background regions. Although effective in avoiding color fidelity compromises in non-background areas, discontinuity between pixels classified as white and non-white may still occur between background and non-background areas.
Accordingly, what is needed in this art are increasingly sophisticated systems and methods for background suppression in the image path of a document reproduction system which provides a smooth transition in chrominance suppression between background and non-background areas.